The present invention relates to method for preparing cured sausage and ham in a completely automatic manner.
Cured sausage, large sausage, smoked pork sausage, etc., are meat products in which the meat is ground to a variable size, depending upon the type of product. The size can range from 20-30 mm for smoked pork sausage, to 2-3 mm for Pamplona smoked pork sausage or large sausage. The sausage contains, in addition, a variable proportion of ground fat, salt spices, and minor quantities of other ingredients.
The mass is packed tightly into a natural or synthetic permeable gut, with the sausage then being subjected to a curing-drying process. This process comprises a fermentation stage and a drying stage.
In the fermentation stage, there is an important microbial development originating from microorganisms which are always present in the meat, or selected seed strains which are added at the time of processing.
In the drying stage, water evaporates from the surface of the gut. This creates a moisture gradient on the inside of the sausage, as a result of which water diffuses towards the external part of the sausage and evaporates therefrom.
Fermentation produces acid (mainly lactic acid) with a resulting fall in pH which, as the pH reaches a value of about 5.4-5.2, induces coagulation of soluble proteins, thus giving rise to hardening of the sausage which acquires texture during the process. In addition, enzymes generated by the microorganisms as the same act upon the meat and the fats, produce changes therein, which result in the development of the typical tastes and aromas characteristic of these products.
As a result of the drying operation, the salts become concentrated and the concentration of water decreases in the sausage. Consequently, together with the decrease in pH previously noted, bacterial activity is hindered until it is completely arrested and the product is stable and can be preserved without refrigeration.
Futhermore, as a result of the drying, consistency and hardness of the sausage increases until the characteristics are obtained which are appropriate for the finished product suitable for consumption.
These two stages are not totally different, although at the beginning, fermentation generally predominates, while at the end, drying is effected.
After the operation involving the packaging of the mass into the gut, the product is often subjected to a heating at low temperature operation which involves maintaining the parts in a chamber with controlled humidity and temperature. In general, the temperatures are relatively high, and range from about 20.degree. to 25.degree. C. These conditions are maintained for about 24 to 28 hours.
This favors a substantial growth of the microorganisms and gives rise to a rapid fall in pH. It is very convenient for the pH to rapidly reach a value of less than 5.5, which impedes the development of undesirable microorganisms which might produce unwanted fermentations of the putrid type, etc.
Once the desired pH has been reached, the drying is continued at a substantially lower temperature (ranging only from about 13.degree. to 17.degree. C.). It is very important for the fall in pH to be perfectly controlled, so that excessively low values (pH lower than about 4.9-5.0) are not reached, because the quality of the product decreases greatly as a result of the formation of acidic aromas and tastes. The firmness of the product itself is also occasionally adversely affected.
The final stage of the heating operation must therefore occur as a function of the pH reached and the rate of fall thereof. It is possible, for example, to correctly terminate the heating operation when the pH reaches a value of 5.2 if the rate of fall is low, since the final pH reached would be, for example, 5.0. However, on the other hand, it might be too late if the rate of fall of the pH is too high, for in that instance, it is probable that final values of about 4.6-4.7 will be reached.
In such cases, which occur less frequently, in which the heating operation is not employed, but in which the sausage is subjected to a relatively low temperature from the beginning, it is also vital to control the pH although the falling thereof will occur much more slowly than in the heating operation.
In order to exert satisfactory control over fermentation, it is necessary to be provided with a curve relative to the fall in pH which will make it possible to determine the appropriate end of the heating operation.
However, this is not sufficient to ensure the perfect curing for when the more active fermentation stage has ended and the pH remains constant or shows very little variation, the major part of the drying operation still remains to be executed, which lasts much longer than the heating step.
Correct drying is absolutely essential for production of a high quality sausage. Two problems may occur:
(1) An excessively high rate of drying. If the rate of evaporation is too high when a high proportion of moisture remains in the sausage, then the external layers of the piece of sausage involved will become dehydrated without diffusion of water from the center of the piece being able to compensate for such loss of moisture.
This results in the formation of a thin external ring of well-cured mass with the typical color of dried sausage (shrunken material), while in the internal part of the piece of sausage, the mass remains moist and soft with a much lighter color which very often turns out to be grayish. The aroma and taste are extremely adversely affected;
(2) Excessively slow drying. An excessively slow drying operation with a resulting increase in drying time, has negative economic ramifications due to the high cost of capital immobilized for drying the sausage.
Furthermore, excessively low drying can have undesirable effects on the quality of the sausage. Maintaining of a high humidity inside the pieces of sausage for a prolonged period of time, favors unwanted fermentations which affect aroma, taste and color.
Control of the drying operation is carried out by acting upon the surrounding conditions of temperature and relative humidity, which are the conditions determining the rate of evaporation. The information required to carry out this control involves the knowledge of the weight of the pieces of sausage at each moment. Several sausages are chosen as controls, the weight of which is measured systematically during the process. On the basis of this data, weight loss from the beginning of the drying operation, as well as the value of the rate of decrease during each time interval, can be calculated.
Presently, monitoring of curing chambers for the sausage is effected manually on the basis of information obtained concerning the evolution of pH and contraction of the items or pieces of sausage.
During the heating operation, at the beginning of the process, the pH of the pieces is measured manually from time to time. On the basis of this data so obtained, it has been possible to calculate the absolute value of shrinkage, as well as the rate of shrinkage. The weight is monitored until the end of the curing process.
With this data, technical personnel in charge of the operation can make decisions, i.e. decide that the heating operation has been completed, increase or decrease in the temperature is warranted to accelerate or slow down the fermentation, increase or decrease in the rate of shrinkage is required, decrease in the relative humidity and/or increase in the temperature is required, or to the contrary, increase in the relative humidity and/or decrease in the temperature is warranted.
Although modern curing chambers have been used, it has been necessary to carry out this monitoring manually.
The only function of automatic control had been to maintain the two parameters to be controlled (relative humidity and temperature) between the minimum and maximum values which were previously manually set.
On the basis of such information regarding pH and weight obtained for the sausage, the technical personnel could decide whether or not to change the prescribed limits. In other words, the monitoring of the process did not include any "feed-back" loop or, i.e. this loop was effected manually.